my undo doesn't work in 2.8, except in edit mode
There is (and in 2.79 also have been) two Undo handling behaviors, which can be triggered using the Global Undo property in the Preferences. Go to your Preferences, navigate to Editing, and make sure Global Undo is checked there to get back to the undo behavior you are used to:



In 2.79, when Global Undo is unchecked, only edit mode changes would be recorded on the Undo Stack. Object mode changes then cannot be undone. In 2.80, at the moment the behavior you described is used, but this might change until final release.